Due to recent improvements in charge-discharge characteristics of a lead storage battery, there is renewed interest in this type of battery as a high performance power supply in industrial areas where expensive lithium ion secondary batteries make poor business sense. Specialized electric vehicles such as electric carts and forklift trucks, and so on, are handled in these industrial areas rather than portable battery-equipped devices. Further, in these industrial areas, systems for recycling battery-equipped device main bodies and lead storage batteries are well established.
A charge acceptance of a lead storage battery is affected by a temperature to which the battery is exposed. When the lead storage battery is exposed to a low temperature, for example, reductions occur in electrolyte fluidity and electrode reactivity. Accordingly, reaction resistance increases, leading to a reduction in the charge acceptance. Here, the reaction resistance means how easily an electrochemical reaction occurs in the battery. When the battery is exposed to a low temperature, for example, the reaction resistance increases, since an electrochemical reaction is less likely to occur. Conversely, when the battery is exposed to a high temperature, the reaction resistance decreases, since an electrochemical reaction is more likely to occur.
When the lead storage battery is continuously undercharged, sulfation (a phenomenon whereby lead sulfate obtained as a discharge product becomes inactive such that a battery capacity is impaired) advances. When the lead storage battery is continuously overcharged, on the other hand, grid corrosion occurs particularly in a positive electrode, leading to a reduction in life. To charge the lead storage battery appropriately, therefore, it is necessary to learn the temperature to which the lead storage battery is exposed precisely and reflect the learned temperature in charging conditions.
Patent Document 1 describes controlling charging and discharging by measuring each temperature to which a lead storage battery is exposed and calculating a charging control voltage after reflecting a resulting measured value in an equation having the temperature as a variable. Patent Document 2 describes multistage constant current charging having three or more stages, in which a charging current is reduced and a following stage of the charging is started when a lead storage battery reaches a predetermined end-of-charge voltage, and a final stage of the charging is performed until a predetermined time elapses after the lead storage battery reaches the end-of-charge voltage (a charging current In, where n is the number of charging stages, corresponds to I1>I2> . . . >In−1). In Patent Document 2, the charging is controlled appropriately by increasing the end-of-charge voltage as the temperature to which the lead storage battery is exposed decreases.    Patent Document 1: Japanese Patent Application Publication H10-032020    Patent Document 2: Japanese Patent Application Publication H11-089104